Photoconductive antenna, terahertz wave generating device, camera, imaging device, and measuring device

ABSTRACT

A photoconductive antenna is adapted to generate terahertz waves when irradiated by pulsed light. The photoconductive antenna includes a semiconductor layer, a first conductive layer, a second conductive layer, a first electrode and a second electrode. The first conductive layer is disposed on a first surface of the semiconductor layer. The second conductive layer is disposed on the first surface of the semiconductor layer with a prescribed gap being formed between the first conductive layer and the second conductive layer. The first electrode is electrically connected to the first conductive layer. The second electrode is electrically connected to the second conductive layer. The first conductive layer contains a first conductive type impurity. The second conductive layer contains a second conductive type impurity. The semiconductor layer has a carrier density lower than a carrier density of the first conductive layer or a carrier density of the second conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.14/504,643 filed on Oct. 2, 2014, which is a continuation application ofU.S. application Ser. No. 13/721,960 filed on Dec. 20, 2012, now U.S.Pat. No. 8,878,134. This application claims priority to Japanese PatentApplication No. 2012-007939 filed on Jan. 18, 2012. The entiredisclosures of U.S. application Ser. Nos. 14/504,643 and 13/721,960 andJapanese Patent Application No. 2012-007939 are hereby incorporatedherein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a photoconductive antenna, a terahertzwave generating device, a camera, an imaging device, and a measuringdevice.

2. Related Art

In recent years, attention has been devoted to terahertz waves, whichare electromagnetic waves with frequencies of 100 GHz or greater and 30THz or less. Terahertz waves can be used in various forms of measurementand non-destructive testing such as imaging and spectrometry.

The terahertz wave generating device that generates these terahertzwaves has a light source device that generates light pulses (pulsedlight) having pulse widths at the approximately sub picosecond level(several hundred femtoseconds) and a photoconductive antenna thatgenerates terahertz waves by irradiating light pulses generated by thelight pulse generator.

As the photoconductive antenna, for example, disclosed in JapaneseLaid-Open Patent Application Publication No. 2010-50287 is a pinstructure photoconductive element (photoconductive antenna) which has ann type semiconductor layer, an i type semiconductor layer, and a p typesemiconductor layer. With this photoconductive antenna, the n typesemiconductor layer is provided at one surface side of the i typesemiconductor layer, and the p type semiconductor layer is provided atthe other surface side. Also, the n type semiconductor layer and the ptype semiconductor layer are arranged to be skewed in relation to eachother in the thickness direction of the i type semiconductor layer. Notethat the terahertz waves are emitted in the direction perpendicular tothe direction of the electric field.

With the photoconductive antenna noted in the above mentionedpublication, for a dipole shaped photoconductive antenna (PCA)manufactured using a low temperature growth GaAs (LT-GaAs) substrate, itis possible to make the intensity of the generated terahertz wavesapproximately 10 times larger.

SUMMARY

With the photoconductive antenna noted in the above mentionedpublication, the n type semiconductor layer is provided on one surfaceside of the i type semiconductor layer, and the p type semiconductorlayer is provided on the other surface side, so the electric fielddirection changes according to variation in the thickness of the i typesemiconductor during manufacturing, and because of that, there is theproblem that variation occurs in the terahertz wave emission direction.

An object of the present invention is to provide a photoconductiveantenna, a terahertz wave generating device, a camera, an imagingdevice, and a measuring device capable of suppressing variation in theemission direction, and generating high intensity terahertz waves.

A photoconductive antenna according to one aspect is adapted to generateterahertz waves when irradiated by pulsed light. The photoconductiveantenna includes a semiconductor layer, a first conductive layer, asecond conductive layer, a first electrode and a second electrode. Thefirst conductive layer is disposed on a first surface of thesemiconductor layer. The second conductive layer is disposed on thefirst surface of the semiconductor layer with a prescribed gap beingformed between the first conductive layer and the second conductivelayer. The first electrode is electrically connected to the firstconductive layer. The second electrode is electrically connected to thesecond conductive layer. The first conductive layer contains a firstconductive type impurity. The second conductive layer contains a secondconductive type impurity. The semiconductor layer has a carrier densitylower than a carrier density of the first conductive layer or a carrierdensity of the second conductive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a drawing showing a terahertz wave generating device(photoconductive antenna) according to a first embodiment of the presentinvention as taken along a section line S-S in FIG. 2.

FIG. 2 is a top plan view of the photoconductive antenna of theterahertz wave generating device shown in FIG. 1.

FIG. 3A is a top plan view of the n type semiconductor layer and the ptype semiconductor layer of the photoconductive antenna of the terahertzwave generating device shown in FIG. 1.

FIG. 3B is a top plan view of the n type semiconductor layer and the ptype semiconductor layer of the photoconductive antenna in analternative embodiment.

FIG. 4 is a cross section perspective view of the light source device ofthe terahertz wave generating device shown in FIG. 1.

FIG. 5 is a cross section view of the light source device as taken alonga section line A-A in FIG. 4.

FIG. 6 is a cross section view of the light source device as taken alonga section line B-B in FIG. 4.

FIGS. 7A to 7D are cross section diagrams for describing one example ofthe manufacturing method of the photoconductive antenna of the terahertzwave generating device shown in FIG. 1.

FIGS. 8A to 8C are cross section diagrams for describing one example ofthe manufacturing method of the photoconductive antenna of the terahertzwave generating device shown in FIG. 1.

FIG. 9 is a cross section diagram of a photoconductive antenna accordingto a second embodiment of the present invention.

FIG. 10 is a cross section diagram of a photoconductive antennaaccording to a third embodiment of the present invention.

FIG. 11 is a cross section diagram of a photoconductive antennaaccording to a fourth embodiment of the present invention.

FIGS. 12A to 12C are cross section diagrams for describing an example ofthe manufacturing method of the photoconductive antenna shown in FIG.11.

FIG. 13 is a block diagram showing an embodiment of the imaging deviceof the present invention.

FIG. 14 is a top plan view showing the terahertz wave detecting unit ofthe imaging device shown in FIG. 13.

FIG. 15 is a graph showing the spectrum in the terahertz band of theobject.

FIG. 16 is a drawing of the image showing the distribution of substancesA, B, and C of the object.

FIG. 17 is a block diagram showing an embodiment of the measuring deviceof the present invention.

FIG. 18 is a block diagram showing an embodiment of the camera of thepresent invention.

FIG. 19 is a schematic perspective view showing an embodiment of thecamera of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Following, a detailed description of the photoconductive antenna, theterahertz wave generating device, the camera, the imaging device, andthe measuring device of the present invention will be provided based onpreferred embodiments shown in the attached drawings.

First Embodiment

FIG. 1 is a drawing showing the terahertz wave generating deviceaccording to the first embodiment of the present invention. With thisFIG. 1, a cross section view taken along a section line S-S in FIG. 2 isshown for the photoconductive antenna, and a block diagram is shown forthe light source device. FIG. 2 is a top plan view of thephotoconductive antenna of the terahertz wave generating device shown inFIG. 1. FIG. 3A is a top plan view of the n type semiconductor layer andthe p type semiconductor layer of the photoconductive antenna of theterahertz wave generating device shown in FIG. 1, while FIG. 3B shows atop plan view of the n type semiconductor layer and the p typesemiconductor layer of the photoconductive antenna of the terahertz wavegenerating device in an alternative embodiment. FIG. 4 is a crosssection perspective view of the light source device of the terahertzwave generating device shown in FIG. 1. FIG. 5 is a cross section viewtaken along a section line A-A in FIG. 4. FIG. 6 is a cross section viewtaken along a section line B-B in FIG. 4. FIGS. 7A to 7D and FIGS. 8A to8C are cross section views for describing an example of themanufacturing method of the photoconductive antenna of the terahertzwave generating device shown in FIG. 1. Note that hereafter, in FIG. 1and FIG. 4 to FIG. 8, the upper side will be described as “upper” andthe lower side will be described as “lower.”

As shown in FIG. 1, the terahertz wave generating device 1 has a lightsource device 3 that generates light pulses (pulsed light) which isexcitation light, and a photoconductive antenna 2 for generatingterahertz waves by irradiating light pulses generated by the lightsource device 3. A terahertz wave means an electromagnetic wave forwhich the frequency is 100 GHz or greater and 30 THz or less, andparticularly an electromagnetic wave of 300 GHz or greater and 3 THz orless.

As shown in FIG. 4 to FIG. 6, with this embodiment, the light sourcedevice 3 has a light pulse generator 4 that generates light pulses, afirst pulse compressor 5 that performs pulse compression on light pulsesgenerated by the light pulse generator 4, a second pulse compressor 7that performs pulse compression on light pulses for which pulsecompression was done by the first pulse compressor 5, and an amplifier 6that amplifies the light pulses.

The amplifier 6 can be provided at the front stage of the first pulsecompressor 5, or between the first pulse compressor 5 and the secondpulse compressor 7, but with the configuration in the drawing, theamplifier 6 is provided between the first pulse compressor 5 and thesecond pulse compressor 7. With this configuration, the light pulseswhich underwent pulse compression by the first pulse compressor 5 areamplified by the amplifier 6, and the light pulses amplified by theamplifier 6 undergo pulse compression by the second pulse compressor 7.

Also, the pulse width (half-value width) of the light pulses emittedfrom the light source device 3 is not particularly restricted, but ispreferably 1 femtosecond or greater and 800 femtoseconds or less, andmore preferably 10 femtoseconds or greater and 200 femtoseconds or less.

Also, the frequency of the light pulses emitted from the light sourcedevice 3 is set to the same or greater frequency corresponding to theband gap of the i type semiconductor layer 24 of the photoconductiveantenna 2 described later.

Also, the light pulse generator 4 can use a so-called semiconductorlaser such as a DBR laser, DFB laser, mode locked laser or the like, forexample. The pulse width of the light pulses generated by this lightpulse generator 4 is not particularly restricted, but is preferably 1picosecond or greater and 100 picoseconds or less.

Also, the first pulse compressor 5 performs pulse compression based onsaturable absorption. Specifically, the first pulse compressor 5 has asaturable absorber, and using that saturable absorber, light pulses arecompressed and pulse width is decreased.

Also, the second pulse compressor 7 performs pulse compression based ongroup velocity dispersion compensation. Specifically, the second pulsecompressor 7 has a group velocity dispersion compensation medium, andwith this embodiment a coupled waveguide structure, and using thatcoupled waveguide structure, light pulses are compressed and pulse widthis decreased.

Also, the light pulse generator 4 of the light source device 3, thefirst pulse compressor 5, the amplifier 6, and the second pulsecompressor 7 are made into an integral unit, specifically, integrated onthe same substrate.

In specific terms, the light source device 3 has a substrate 31 which isa semiconductor substrate, a cladding layer 32 which is provided on thesubstrate 31, an active layer 33 which is provided on the cladding layer32, a waveguide structure processing etching stop layer 34 provided onthe active layer 33, a cladding layer 35 provided on the waveguidestructure processing etching stop layer 34, a contact layer 36 providedon the cladding layer 35, an insulation layer 37 provided on thewaveguide structure processing etching stop layer 34, a cladding layer32 side electrode 38 provided on the surface of the substrate 31, andcladding layer 35 side electrodes 391, 392, 393, 394, and 395 providedon the contact layer 36 and the insulation layer 37 surface. Also, adiffraction grating 30 is provided between the waveguide structureprocessing etching stop layer 34 of the light pulse generator 4 and thecladding layer 35. Note that the waveguide structure processing etchingstop layer is not limited to being provided directly above the activelayer, but can also be provided within the cladding layer, for example.

The structural materials of each part are not particularly restricted,but an example for the substrate 31 and the contact layer 36 is GaAs orthe like. Also, an example for the cladding layers 32 and 35, thewaveguide structure processing etching stop layer 34, and thediffraction grating 30 includes AlGaAs or the like. Also, for the activelayer 33, an example is a structure using a quantum effect called amultiple quantum well or the like. In specific terms, an example of theactive layer 33 is an item with a structure called a distributed indexof refraction multiple quantum well structured with multiple quantumwells or the like made by alternately providing a plurality of welllayers (GaAs well layers) and barrier layers (AlGaAs barrier layers) orthe like.

With the constitution in the drawing, the waveguide of the light sourcedevice 3 is constituted from the cladding layer 32, the active layer 33,the waveguide structure processing etching stop layer 34, and thecladding layer 35. Also, the cladding layer 35 is provided in a shapecorresponding to the waveguide, only on the top part of the waveguide.Also, the cladding layer 35 is formed by removal of the unnecessaryparts by etching. Depending on the manufacturing method, it is possibleto omit the waveguide structure processing etching stop layer 34.

Also, two each of the cladding layer 35 and the contact layer 36 areprovided. One of the cladding layer 35 and the contact layer 36constitute the light pulse generator 4, the first pulse compressor 5,the amplifier 6, and part of the second pulse compressor 7, and areprovided sequentially, and the other cladding layer 35 and contact layer36 constitute part of the second pulse compressor 7. Specifically, onepair of cladding layers 35 and one pair of contact layers 36 areprovided on the second pulse compressor 7.

Also, the electrode 391 is provided so as to correspond to the claddinglayer 35 of the light pulse generator 4, the electrode 392 is providedso as to correspond to the cladding layer 35 of the first pulsecompressor 5, the electrode 393 is provided so as to correspond to thecladding layer 35 of the amplifier 6, and the electrodes 394 and 395 areprovided so as to respectively correspond to the two cladding layers 35of the second pulse compressor 7. The electrode 38 is a shared electrodeof the light pulse generator 4, the first pulse compressor 5, theamplifier 6, and the second pulse compressor 7. Then, the pair ofelectrodes of the light pulse generator 4 is constituted by theelectrode 38 and the electrode 391, the pair of electrodes of the firstpulse compressor 5 is constituted by the electrode 38 and the electrode392, the pair of electrodes of the amplifier 6 is constituted by theelectrode 38 and the electrode 393, and the two pairs of electrodes ofthe second pulse compressor 7 are constituted by the electrode 38 andelectrode 394 and the electrode 38 and electrode 395.

The overall shape of the light source device 3 is a rectangular solidwith the constitution in the drawing, but naturally it is not restrictedto this.

Also, the dimensions of the light source device 3 are not particularlyrestricted, but for example can be 1 mm or greater and 10 mm or less×0.5mm or greater and 5 mm or less×0.1 mm or greater and 1 mm or less.

With the present invention, it also goes without saying that theconstitution of the light source device is not restricted to thepreviously described constitution.

Next, the photoconductive antenna 2 will be described.

As shown in FIG. 1 and FIG. 2, the photoconductive antenna 2 has an ntype semiconductor layer (first conductive region) 22, an i typesemiconductor layer (semiconductor region) 24 for generating terahertzwaves, a p type semiconductor layer (second conductive region) 23, andan electrode (first electrode) 28 and an electrode (second electrode) 29constituting the pair of electrodes. The i type semiconductor layer 24supports the n type semiconductor layer 22, the p type semiconductorlayer 23, and the electrodes 28 and 29, and also acts as a substratemainly to provide rigidity. Specifically, the n type semiconductor layer22 and the p type semiconductor layer 23 are provided on the i typesemiconductor layer 24, the electrode 28 is provided on the n typesemiconductor layer 22, and the electrode 29 is provided on the p typesemiconductor layer 23.

The i type semiconductor layer 24 does not have to also act as asubstrate, and it is possible for the photoconductive antenna 2 to havea separate substrate and have the i type semiconductor layer providedonly on the necessary sites.

Also, with the configuration in the drawing, the shape of the i typesemiconductor layer 24 is rectangular when seen from the direction atwhich the light pulses are made incident. The shape of the i typesemiconductor layer 24 is not restricted to being rectangular, and canalso be a circle, an oval, or another polygon or the like such as atriangle, a pentagon, a hexagon or the like. Hereafter, “when seen fromthe direction at which the light pulses are made incident” or “when seenfrom the layer thickness direction of each semiconductor layer” is alsocalled “the planar view.”

This i type semiconductor layer 24 is constituted with a semiconductormaterial. The semiconductor material constituting this i typesemiconductor layer 24 is preferably an intrinsic semiconductor, but mayalso include a small volume of a p type impurity or an n type impurity.In other words, the i type semiconductor layer 24 can be said to have acarrier density lower than the n type semiconductor layer 22 when itcontains an n type impurity, and can be said to have a carrier densitylower than the p type semiconductor layer 23 when it contains a p typeimpurity. It is preferable that even when the i type semiconductor layer24 contains either an n type impurity or a p type impurity, the carrierdensity is lower than with the n type semiconductor layer 22 and the ptype semiconductor layer 23.

In specific terms, the carrier density of the i type semiconductor layer24 is preferably 1×10¹⁸ cm³ or less, more preferably 1×10¹²/cm³ orgreater and 1×10¹⁸/cm³ or less, and even more preferably 1×10¹²/cm³ orgreater and 1×10¹⁶/cm³ or less.

Also, the n type semiconductor layer 22 and the p type semiconductorlayer 23 are arranged via a prescribed gap 25 on the i typesemiconductor layer 24. With this configuration, in the top plan view,at least a portion of the i type semiconductor layer 24 is arranged atthe gap 25 between the n type semiconductor layer 22 and the p typesemiconductor layer 23. With this embodiment, a portion of the i typesemiconductor layer 24 is arranged at that gap 25, and that gap 25 isfilled (embedded) by a portion of the i type semiconductor layer 24. Itis possible to generate higher intensity terahertz waves. With thisterahertz wave generating device 1, the light pulses generated by thelight source device 3 are made to be irradiated on the i typesemiconductor layer 24 via the gap 25 and positioned within that gap 25.Therefore, the surface of the i type semiconductor layer 24 at the gap25 (an interfacial surface with the air layer) constitutes the plane ofincidence at which the light pulses are made incident.

In specific terms, the n type semiconductor layer 22 light pulseincidence side surface 221 (an interfacial surface with the electrode28: a first interfacial surface in this embodiment), the p typesemiconductor layer 23 light pulse incidence side surface 231 (aninterfacial surface with the electrode 29: a first interfacial surfacein this embodiment), and the light pulse incidence side surface 241 ofthe site positioned at the gap 25 of the i type semiconductor layer 24(the interfacial surface) are arranged within the same plane (samesurface) (i.e., the surface 241 is flush with the surface 221 and thesurface 231). Then, the n type semiconductor layer 22 terahertz waveemission side surface 222 facing opposite the surface 221 (aninterfacial surface with the i type semiconductor layer 24: a secondinterfacial surface in this embodiment) and the p type semiconductorlayer 23 terahertz wave emission side surface 232 facing opposite thesurface 231 (an interfacial surface with the i type semiconductor layer24: a second interfacial surface in this embodiment) are arranged withinthe same plane. Specifically, the one interfacial surface of the n typesemiconductor layer 22 and the one interfacial surface of the p typesemiconductor layer 23 are arranged within the same surface, and theother interfacial surface of the n type semiconductor layer 22 and theother interfacial surface of the p type semiconductor layer 23 arearranged on the same side with respect to the previously described sameplane (surface 241 at the gap 25 of the i type semiconductor layer 24).Hereafter, the light pulse incidence side surface is also called the“incidence side surface,” and the terahertz wave emission side surfaceis also called the “emission side surface.”

Also, the n type semiconductor layer 22 is constituted from asemiconductor material containing an n type (first conductive type)impurity. The carrier density (impurity concentration) of the n typesemiconductor layer 22 is preferably 1×10¹⁷/cm³ or greater, morepreferably 1×10²⁰/cm³ or greater, and even more preferably 1×10²⁰/cm³ orgreater and 1×10²⁵/cm³ or less. The n type impurity is not particularlyrestricted, but examples include Si, Ge, S, Se or the like.

Also, the p type semiconductor layer 23 is constituted by asemiconductor material containing a p type (second conductive type)impurity. The carrier density of the p type semiconductor layer 23 ispreferably 1×10¹⁷/cm³ or greater, more preferably 1×10²⁰/cm³ or greater,and even more preferably 1×10²⁰/cm³ or greater and 1×10²⁵/cm³ or less.This p type impurity is not particularly restricted, but examplesinclude Zn, Mg, C or the like.

The n type semiconductor layer 22 and the p type semiconductor layer 23can respectively be formed by, for example, doping a p type impurity inthe i type semiconductor layer 24 using an ion implantation method, adiffusion method or the like. Specifically, the n type semiconductorlayer 22 or the p type semiconductor layer 23 become areas in which ntype or p type impurities are implanted at a designated depth along thesurface of the i type semiconductor layer 24, so it is possible to forma layer shaped n type or p type semiconductor region.

The semiconductor material of the n type semiconductor layer 22, the ptype semiconductor layer 23, and the i type semiconductor layer 24 isnot particularly restricted, and it is possible to use various types ofitems, but it is preferable to use a III-V compound semiconductor. Also,the III-V compound semiconductor is not particularly restricted, andexamples include GaAs, InP, InAs, InSb and the like.

With this kind of pin structure using the n type semiconductor layer 22,the i type semiconductor layer 24, and the p type semiconductor layer23, the withstand voltage is improved, and this makes it possible toform a larger electric field, and thus, it is possible to generatehigher intensity terahertz waves.

Also, the positional relationship of the n type semiconductor layer 22and the p type semiconductor layer 23 is fixed without relying on thethickness of the i type semiconductor layer 24, so it is possible tomake the electric field direction fixed, and with this configuration, itis possible to make the terahertz wave emission direction fixed.

The shape of the n type semiconductor layer 22 and the p typesemiconductor layer 23 are respectively not particularly restricted, butwith this embodiment, as shown in FIG. 3A, the n type semiconductorlayer 22 is constituted by a band shaped part 224 in a band shape, and aprojecting part 223 provided midway in the band shaped part 224,specifically, in its middle part, and projecting to the p typesemiconductor layer 23 side. Also, as shown in FIG. 3B, the projectingpart 223 may also be provided at the end part of the band shaped part224. With the constitution in the drawing, with the planar view, theshape of the projecting part 223 is a rectangular shape. The shape ofthe projecting part 223 is not restricted to being rectangular, and canalso be a circle, an oval, or another polygon or the like such as atriangle, a pentagon, a hexagon or the like.

Also, with this embodiment, the p type semiconductor layer 23 has ashape that is the reverse of the n type semiconductor layer 22.Specifically, as shown in FIG. 3A, the p type semiconductor layer 23 isconstituted by a band shaped part 234 in a band shape, and a projectingpart 233 provided midway in the band shaped part 234, specifically, inits middle part, and projecting to the n type semiconductor layer 22side. Also, as shown in FIG. 3B, the projecting part 233 may also beprovided on the end part of the band shaped part 234. With theconstitution in the drawing, with the planar view, the shape of theprojecting part 233 is a rectangular shape. The shape of the projectingpart 233 is not restricted to being rectangular, and can also be acircle, an oval, or another polygon or the like such as a triangle, apentagon, a hexagon or the like.

The n type semiconductor layer 22 and the p type semiconductor layer 23are arranged such that the band shaped part 224 of the n typesemiconductor layer 22 and the band shaped part 234 of the p typesemiconductor layer 23 are parallel.

Also, the thickness d1 of the n type semiconductor layer 22 and thethickness d2 of the p type semiconductor layer 23 are not particularlyrestricted, and are set as appropriate according to various conditions,but are preferably 10 nm or greater and 1 μm or less. The thickness d1of the n type semiconductor layer 22 and the thickness d2 of the p typesemiconductor layer 23 may be the same or may be different, but withthis embodiment, they are set to be the same.

Also, the distance (gap distance) d of the gap 25 between the n typesemiconductor layer 22 and the p type semiconductor layer 23 is notparticularly restricted, and is set as appropriate according to variousconditions, but is preferably 1 μm or greater and 10 μm or less.

Also, the width w1 of the projecting part 223 of the n typesemiconductor layer 22 and the width w2 of the projecting part 233 ofthe p type semiconductor layer 23 are not particularly restricted, andare set as appropriate according to various conditions, but arepreferably 1 μm or greater and 10 μm or less. The width w1 of theprojecting part 223 of the n type semiconductor layer 22 and the widthw2 of the projecting part 233 of the p type semiconductor layer 23 maybe the same, or may be different, but with this embodiment, they are setto be the same.

Also, the electrode 28 is provided on the n type semiconductor layer 22.Specifically, the electrode 28 is in contact with the n typesemiconductor layer, and is electrically connected to that n typesemiconductor layer 22.

Also, the electrode 29 is provided on the p type semiconductor layer 23.Specifically, the electrode 29 is in contact with the p typesemiconductor layer 23, and is electrically connected to that p typesemiconductor layer 23.

Also, the respective shapes of the electrodes 28 and 29 are notparticularly restricted, but with this embodiment, the electrode 28 andthe n type semiconductor layer 22 have the same shape. With thisconfiguration, it is possible to lower the contact resistance betweenthe electrode 28 and the n type semiconductor layer 22, and to reducethe power consumption. In specific terms, the electrode 28 has a bandshape, and is constituted by a band shaped part 282 that functions aswiring, and a projecting part 281 provided midway in the band shapedpart 282, specifically, at the middle part, that projects to theelectrode 29 side. With the constitution in the drawing, with the planarview, the shape of the projecting part 281 is a rectangle. The shape ofthe projecting part 281 is not restricted to being rectangular, and canalso be a circle, an oval, or another polygon or the like such as atriangle, a pentagon, a hexagon or the like.

With this embodiment, the electrode 29 and the p type semiconductorlayer 23 have the same shape. With this configuration, it is possible tolower the contact resistance between the electrode 29 and the p typesemiconductor layer 23, and to reduce the power consumption.Specifically, the electrode 29 has a shape that is the reverse of the ntype semiconductor layer 22. In specific terms, the electrode 29 has aband shape, and is constituted by a band shaped part 292 that functionsas wiring, and a projecting part 291 provided midway in the band shapedpart 292, specifically, at the middle part, that projects to theelectrode 28 side. With the constitution in the drawing, in the top planview, the shape of the projecting part 291 is a rectangle. The shape ofthe projecting part 291 is not restricted to being rectangular, and canalso be a circle, an oval, or another polygon or the like such as atriangle, a pentagon, a hexagon or the like.

The electrode 28 and the electrode 29 are arranged such that the bandshaped part 282 of the electrode 28 and the band shaped part 292 of theelectrode 29 are parallel.

A power supply device 18 is electrically connected to the electrodes 28and 29 respectively via a pad, conducting wire, connector or the like(not illustrated), and direct current voltage is applied between theelectrode 28 and the electrode 29 so that the electrode 28 side ispositive.

Next, an example of the manufacturing method of the photoconductiveantenna 2 of the terahertz wave generating device 1 will be described.

First, as shown in FIG. 7A, a resist layer 81 is formed on the topsurface of the i type semiconductor layer 24, and the resist layer 81 isremoved at the sites at which the p type semiconductor layer 23 isformed on the top surface of the i type semiconductor layer 24.

Next, as shown in FIG. 7B, a p type impurity is doped in the i typesemiconductor layer 24 using an ion implantation method, diffusionmethod or the like, for example. With this configuration, the p typesemiconductor layer 23 is formed. Then, the resist layer 81 is removed.

Next, as shown in FIG. 7C, a resist layer 82 is formed on the i typesemiconductor layer 24 and the p type semiconductor layer 23 topsurface, and the resist layer 82 is removed at the sites at which the ntype semiconductor layer 22 is formed on the top surface of the i typesemiconductor layer 24.

Next, as shown in FIG. 7D, an n type impurity is doped in the i typesemiconductor layer 24 using an ion implantation method, diffusionmethod or the like, for example. With this configuration, the n typesemiconductor layer 22 is formed. Then, the resist layer 82 is removed.

Next, as shown in FIG. 8A, a resist layer 83 is formed on the i typesemiconductor layer 24, the p type semiconductor layer 23, and the ntype semiconductor layer 22 top surface, the resist layer 83 of the topsurface of the p type semiconductor layer 23 and the n typesemiconductor layer 22 is removed, and the resist layer 83 remains onlyon the top surface of the i type semiconductor layer 24.

Next, as shown in FIG. 8B, a metal layer 84 is formed on the p typesemiconductor layer 23, the n type semiconductor layer 22, and theresist layer 83 top surface. The constitutional material of this metallayer 84 is the same as the constitutional material of the electrodes 28and 29.

Next, as shown in FIG. 8C, the resist layer 83 is removed for each metallayer 84 formed on the top surface thereof. With this configuration, theelectrodes 28 and 29 are formed. By doing as described above, thephotoconductive antenna 2 is manufactured.

Next, the operation of the terahertz wave generating device 1 will bedescribed.

With the terahertz wave generating device 1, first, light pulses aregenerated by the light pulse generator 4 of the light source device 3.The pulse width of the light pulses generated by the light pulsegenerator 4 is larger than the target pulse width. The light pulsesgenerated by the light pulse generator 4 pass through the waveguide, andpass through the first pulse compressor 5, the amplifier 6, and thesecond pulse compressor 7 sequentially in that order.

First, at the first pulse compressor 5, pulse compression based onsaturable absorption is performed on the light pulses, and the pulsewidth of the light pulses is decreased. Next, at the amplifier 6, thelight pulses are amplified. Finally, at the second pulse compressor 7,pulse compression based on group velocity dispersion compensation isperformed on the light pulses, and the pulse width of the light pulsesis decreased. In this way, light pulses of the target pulse width aregenerated, and are emitted from the second pulse compressor 7.

The light pulses emitted from the light source device 3 are irradiatedon the surface of the i type semiconductor layer 24 at the gap 25 of thephotoconductive antenna 2, and terahertz waves are generated by that itype semiconductor layer 24. These terahertz waves are emitted from thebottom surface of the i type semiconductor layer 24, specifically, fromthe emission plane.

As described above, with this terahertz wave generating device 1, withthe pin structure, the withstand voltage is increased, and with thisconfiguration, it is possible to form a larger electric field, and as aresult, it is possible to generate higher intensity terahertz waves.

Also, the positional relationship of the n type semiconductor layer 22and the p type semiconductor layer 23 is fixed without depending on thethickness of the i type semiconductor layer 24, so it is possible to fixthe direction of the electric field, and with this configuration, it ispossible to fix the emission direction of the terahertz waves.

Also, the light source device 3 has the first pulse compressor 5, theamplifier 6, and the second pulse compressor 7, so it is possible tomake the light source device 3 more compact, and thus the terahertz wavegenerating device 1 more compact, and it is also possible to generatelight pulses with a desired wave height and desired width, and with thisconfiguration, it is possible to reliably generate the desired terahertzwaves.

With this embodiment, in the top plan view, the electrode 28 and the ntype semiconductor layer 22 have the same shape, but it is alsoacceptable for the electrode 28 and the n type semiconductor layer 22 tonot have the same shape.

Also, with this embodiment, in the top plan view, the electrode 29 andthe p type semiconductor layer 23 have the same shape, but it is alsoacceptable for the electrode 29 and the p type semiconductor layer 23 tonot have the same shape.

In specific terms, for example, it is also possible to omit the bandshaped part 224 of the n type semiconductor layer 22, and to constitutethe n type semiconductor layer 22 using the projecting part 223.Similarly, it is also possible to omit the band shaped part 234 of the ptype semiconductor layer 23, and to constitute the p type semiconductorlayer 23 using the projecting part 233.

Also, for example, it is possible to omit the projecting part 281 of theelectrode 28, and to constitute the electrode 28 using the band shapedpart 282. Similarly, it is possible to omit the projecting part 291 ofthe electrode 29, and to constitute the electrode 29 using the bandshaped part 292.

Also, for example, it is possible to omit the band shaped part 224 ofthe n type semiconductor layer 22 and constitute the n typesemiconductor layer 22 using the projecting part 223, and to omit theprojecting part 281 of the electrode 28 and constitute the electrode 28using the band shaped part 282. Similarly, it is possible to omit theband shaped part 234 of the p type semiconductor layer 23 and constitutethe p type semiconductor layer 23 using the projecting part 233, and toomit the projecting part 291 of the electrode 29 and constitute theelectrode 29 using the band shaped part 292.

Second Embodiment

FIG. 9 is a cross section diagram showing a photoconductive antenna 2Aaccording to the second embodiment of the present invention. Hereafter,in FIG. 9, the upper side will be described as “upper” and the lowerside will be described as “lower.”

Hereafter, the description of the second embodiment will focus on thedifferences from the first embodiment, and a description will be omittedfor items that are the same.

As shown in FIG. 9, with the photoconductive antenna 2A of the secondembodiment, the electrode 28A and the n type semiconductor layer 22 havedifferent shapes, and the electrode 29A and the p type semiconductorlayer 23 have different shapes.

Specifically, the length of the projecting part 223 of the n typesemiconductor layer 22 in the lateral direction of FIG. 9 is set to belonger than the length of the projecting part 281 of the electrode 28Ain the lateral direction of FIG. 9, and the length of the projectingpart 233 of the p type semiconductor layer 23 in the lateral directionof FIG. 9 is set to be longer than the length of the projecting part 291of the electrode 29A in the lateral direction of FIG. 9. With thisconfiguration, it is possible to more reliably prevent the occurrence ofleaked current at the gap 25 between the n type semiconductor layer 22and the p type semiconductor layer 23.

With this photoconductive antenna 2A, the same effects are obtained aswith the previously described first embodiment.

This second embodiment can also be applied to the third and fourthembodiments described later.

Third Embodiment

FIG. 10 is a cross section diagram showing a photoconductive antenna 2Baccording to a third embodiment of the present invention. Hereafter, inFIG. 10, the upper side will be described as “upper” and the lower sidewill be described as “lower.”

Hereafter, the description of the third embodiment will focus on thedifferences from the first embodiment, and a description will be omittedfor items that are the same.

As shown in FIG. 10, with the photoconductive antenna 2B of the thirdembodiment, the n type semiconductor layer 22 terahertz wave emissionside surface 222 (an interfacial surface with the i type semiconductorlayer 24B: a first interfacial surface in this embodiment), the p typesemiconductor layer 23 terahertz wave emission side surface 232 (aninterfacial surface with the i type semiconductor layer 24B: a firstinterfacial surface in this embodiment), and the i type semiconductorlayer 24B incidence side surface 241B (an interfacial surface) arearranged within the same plane (i.e., the surface 241B is flush with thesurface 222 and the surface 232). Then, the n type semiconductor layer22 incidence side surface 221 (an interfacial surface with the electrode28: a second interfacial surface in this embodiment) and the p typesemiconductor layer 23 incidence side surface 231 (an interfacialsurface with the electrode 29: a second interfacial surface in thisembodiment) are arranged within the same plane.

The n type semiconductor layer 22 and the p type semiconductor layer 23can respectively be formed on the i type semiconductor layer 24B usingan epitaxial method or the like, for example. Specifically, for the ntype semiconductor layer 22 or the p type semiconductor layer 23 to beformed at a designated thickness along the surface of the i typesemiconductor layer 24B, it is possible to form a layer shaped n type orp type semiconductor region.

With this photoconductive antenna 2B, the same effects are obtained aswith the previously described first embodiment.

This third embodiment can also be applied to the fourth embodimentdescribed later.

Fourth Embodiment

FIG. 11 is a cross section diagram showing a photoconductive antenna 2Caccording to a fourth embodiment of the present invention. FIGS. 12A to12C are cross section diagrams for describing an example of themanufacturing method of the photoconductive antenna 2C shown in FIG. 11.Hereafter, in FIG. 11 and FIG. 12, the upper side will be described as“upper” and the lower side will be described as “lower.”

Hereafter, the description of the fourth embodiment will focus on thedifferences from the first embodiment, and a description will be omittedfor items that are the same.

As shown in FIG. 11, with the photoconductive antenna 2C of the fourthembodiment, on the i type semiconductor layer 24 at the gap 25 betweenthe electrodes 28 and 29, the n type semiconductor layer 22, and the ptype semiconductor layer 23, an insulation layer (insulation region) 26covering these is provided.

Also, a void part 261 is provided on the insulation layer 26 on the bandshaped part 282 of the electrode 28, exposing a portion of the bandshaped part 282, and with this configuration, a conductive pad part isformed. Similarly, a void part 262 is provided on the insulation layer26 on the band shaped part 292 of the electrode 29, exposing a portionof the band shaped part 292, and with this configuration, a conductivepad part is formed.

With this insulation layer 26, it is possible to more reliably preventthe occurrence of leaked current at the gap 25. Also, it is possible toprevent corrosion or the like of the i type semiconductor layer 24.

The constitutional material of the insulation layer 26 is notparticularly restricted as long as it is an insulating material, andexamples include metal compounds such as SiO₂, SiN, SiON, Al₂O₃ and thelike.

Next, an example of the manufacturing method of the photoconductiveantenna 2C will be described.

As shown in FIG. 8C, the resist layer 83 is removed for each the metallayer 84 formed on the top surface thereof, and up to the point offorming the electrodes 28 and 29 is the same as with the previouslydescribed first embodiment, so the description of the manufacturingmethod up to that point will be omitted.

Next, as shown in FIG. 12A, the insulation layer 26 is formed on theentire top surface of the i type semiconductor layer 24 at the gap 25between the electrodes 28 and 29, the n type semiconductor layer 22, andthe p type semiconductor layer 23.

Next, as shown in FIG. 12B, a resist layer 85 is formed on the topsurface of the insulation layer 26, and the resist layer 85 is removedat the site at which the void parts 261 and 262 are formed on the topsurface of the insulation layer 26.

Next, as shown in FIG. 12C, with the resist layer 85 as a mask, etchingis implemented from the top surface side. Then, the resist layer 85 isremoved. Working in this way, the void part 261 is formed on theinsulation layer 26 on the band shaped part 282 of the electrode 28, andthe void part 262 is formed on the insulation layer 26 on the bandshaped part 292 of the electrode 29. Working as described above, thephotoconductive antenna 2C is manufactured.

With this photoconductive antenna 2C, the same effects as those of thefirst embodiment described above are obtained.

With this embodiment, the insulation layer 26 is provided on the entiretop of the i type semiconductor layer 24 at the gap 25 between theelectrodes 28 and 29, the n type semiconductor layer 22, and the p typesemiconductor layer 23, except for the conductive pad part of theelectrodes 28 and 29, but the invention is not restricted to this, andit is also acceptable to provide it on at least a portion of the i typesemiconductor layer 24 in the gap 25.

Embodiment of Imaging Device

FIG. 13 is a block diagram showing an embodiment of the imaging deviceof the present invention. FIG. 14 is a top plan view showing theterahertz wave detecting unit of the imaging device shown in FIG. 13.FIG. 15 is a graph showing the spectrum of the terahertz band of theobject. FIG. 16 is a drawing of an image showing the distribution of thesubstances A, B, and C of the object.

As shown in FIG. 13, the imaging device 100 is equipped with a terahertzwave generating unit 9, a terahertz wave detecting unit 11 for detectingterahertz waves emitted from the terahertz wave generating unit 9 andpassed through or reflected by the object 150, and an image forming unit12 that generates an image of the object 150, specifically, image data,based on the detection results of the terahertz wave detecting unit 11.The configuration of the terahertz wave generating unit 9 is the same asthe previously noted terahertz wave generating device 1, so adescription will be omitted here.

Also, as the terahertz wave detecting unit 11, an item is used that isequipped with a filter 15 that transmits terahertz waves of targetwavelengths, and a detection unit 17 that detects the terahertz waves ofthe target wavelengths transmitted by the filter 15. Also, as thedetection unit 17, for example, an item is used that converts terahertzwaves to heat and detects it, specifically, an item that convertsterahertz waves to heat, and detects the energy (intensity) of theterahertz waves. As this kind of detection unit, examples includepyroelectric sensors, bolomoters and the like. Naturally, the terahertzwave detecting unit 11 is not restricted to an item of thisconstitution.

Also, the filter 15 has a plurality of pixels (unit filter units) 16arranged two dimensionally. Specifically, the pixels 16 are arranged inmatrix form.

Also, the pixels 16 have a plurality of fields that transmit terahertzwaves of mutually different wavelengths, specifically, a plurality offields that have mutually different transmitted terahertz wavelengths(hereafter also called “transmission wavelengths”). With theconstitution in the drawing, each pixel 16 has a first field 161, asecond field 162, a third field 163, and a fourth field 164.

Also, the detection unit 17 has a first unit detecting unit 171, asecond unit detecting unit 172, a third unit detecting unit 173, and afourth unit detecting unit 174 provided respectively corresponding tothe first field 161, second field 162, third field 163, and fourth field164 of each pixel 16 of the filter 15. Each first unit detecting unit171, second unit detecting unit 172, third unit detecting unit 173, andfourth unit detecting unit 174 respectively convert to heat and detectterahertz waves that were transmitted through the first field 161, thesecond field 162, the third field 163, and the fourth field 164 of eachpixel 16. As a result, at each respective pixel 16, it is possible toreliably detect the terahertz waves of four target wavelengths.

Next, a use example of the imaging device 100 will be described.

First, the object 150 that is the subject of spectral imaging isconstituted by three substances A, B, and C. The imaging device 100performs spectral imaging of this object 150. Also, here, as an example,the terahertz wave detecting unit 11 detects terahertz waves reflectedby the object 150.

With each pixel 16 of the filter 15 of the terahertz wave detecting unit11, a first field 161 and a second field 162 are used.

Also, when the transmission wavelength of the first field 161 is λ1 andthe transmission wavelength of the second field 162 is λ2, and theintensity of the wavelength λ1 component of the terahertz wave reflectedby the object 150 is α1 and the intensity of the transmission wavelengthλ2 component is α2, the transmission wavelength λ1 of the first field161 and the transmission wavelength λ2 of the second field 162 are setso that the difference (α2−α1) between the intensity α2 and intensity α1can be clearly mutually distinguished for the substance A, substance B,and substance C.

As shown in FIG. 15, with substance A, the difference between theintensity α2 of the wavelength λ2 component of the terahertz wavesreflected by the object 150 and the intensity α1 of the wavelength λ1component (α2−α1) is a positive value.

With substance B, the difference between intensity α2 and intensity α1(α2−α1) is zero.

With substance C, the difference between intensity α2 and intensity α1(α2−α1) is a negative value.

With the imaging device 100, when performing spectral imaging of theobject 150, first, terahertz waves are generated by the terahertz wavegenerating unit 9, and those terahertz waves are irradiated on theobject 150. Then, the terahertz wave detecting unit 11 detects theterahertz waves reflected by the object 150 as α1 and α2. Thesedetection results are sent to the image forming unit 12. The detectionof irradiation of terahertz waves on the object 150 and terahertz wavesreflected by the object 150 is performed for the overall object 150.

The image forming unit 12 finds the difference (α2−α1) between theintensity α2 of the wavelength λ2 component of the terahertz wavestransmitted through the second field 162 of the filter 15 and theintensity α1 of the wavelength λ1 component of the terahertz wavestransmitted through the first field 161 based on the detection results.Then, of the object 150, sites for which the difference is a positivevalue are determined and specified as being substance A, sites for whichthe difference is zero as substance B, and sites for which thedifference is a negative value as substance C.

As shown in FIG. 16, the image forming unit 12 creates image data of animage showing the distribution of the substances A, B and C of theobject 150. This image data is sent to a monitor (not illustrated) fromthe image forming unit 12, and an image showing the distribution of thesubstance A, substance B, and substance C of the object 150 is displayedon the monitor. In this case, for example, color coded display is doneso that the field in which substance A of the object 150 is distributedis shown as black, the field in which substance B is distributed isshown as gray, and the field in which substance C is distributed isshown as white. With this imaging device 100, as described above, it ispossible to identify each substance constituting the object 150 and tosimultaneously perform distribution measurement of each substance.

The application of the imaging device 100 is not limited to the itemdescribed above, and for example, it is possible to irradiate terahertzwaves on a person, to detect terahertz waves transmitted or reflected bythat person, and by performing processing at the image forming unit 12,it is possible to determine whether that person is holding a gun, knife,illegal drugs or the like.

Embodiment of Measuring Device

FIG. 17 is a block diagram showing an embodiment of the measuring deviceof the present invention.

Following, the description of the embodiment of the measuring devicewill focus on the differences from the previously described embodimentof the imaging device, the same items will be given the same codenumbers, and a detailed description of those will be omitted.

As shown in FIG. 17, the measuring device 200 is equipped with aterahertz wave generating unit 9 for generating terahertz waves, aterahertz wave detecting unit 11 for detecting terahertz waves emittedfrom the terahertz wave generating unit 9 and transmitted through orreflected by the object 160, and a measuring unit 13 for measuring theobject 160 based on the detection results of the terahertz wavedetecting unit 11.

Next, a use example of the measuring device 200 will be described.

With the measuring device 200, when performing spectroscopic measurementof the object 160, first, terahertz waves are generated by the terahertzwave generating unit 9, and those terahertz waves are irradiated on theobject 160. Then, the terahertz waves transmitted by or reflected by theobject 160 are detected by the terahertz wave detecting unit 11. Thesedetection results are sent to the measuring unit 13. Irradiation of theterahertz waves on the object 160 and detection of the terahertz wavestransmitted by or reflected by the object 160 are performed for theoverall object 160.

With the measuring unit 13, from the detection results, the respectiveintensities of the terahertz waves that were transmitted through thefirst field 161, the second field 162, the third field 163, and thefourth field 164 of the filter 15 are found out, and analysis or thelike of the object 160 components and their distribution is performed.

Embodiment of Camera

FIG. 18 is a block diagram showing the embodiment of the camera of thepresent invention. Also, FIG. 19 shows a schematic perspective viewshowing an embodiment of the camera of the present invention.

Following, the description of the embodiment of the camera will focus onthe differences from the previously described embodiment of the imagedevice, the same items are given the same code numbers as in thepreviously described embodiments, and a detailed description of thosewill be omitted.

As shown in FIG. 18 and FIG. 19, the camera 300 is equipped with aterahertz wave generating unit 9 for generating terahertz waves, aterahertz wave detecting unit 11 for detecting terahertz waves emittedfrom the terahertz wave generating unit 9 and reflected by the object170, and a memory unit 14. Then, each of these parts is housed in a case310 of the camera 300. Also, the camera 300 is equipped with a lens(optical system) 320 for converging (imaging) the terahertz wavesreflected by the object 170 on the terahertz wave detecting unit 11, anda window part 330 for emitting to outside the case 310 the terahertzwaves generated by the terahertz wave generating unit 9. The lens 320and the window part 330 are constituted by members using silicon,quartz, polyethylene or the like that transmit or refract terahertzwaves. The window part 330 can also be constituted with an aperturesimply provided as a slit.

Next, a use example of the camera 300 will be described.

With the camera 300, when taking an image of the object 170, first,terahertz waves are generated by the terahertz wave generating unit 9,and those terahertz waves are irradiated on the object 170. Then, theterahertz waves reflected by the object 170 are converged (imaged) bythe lens 320 to the terahertz wave detecting unit 11 and detected. Thedetection results are sent to and stored in the memory unit 14.Detection of irradiation of the terahertz waves on the object 170 and ofthe terahertz waves reflected by the object 170 is performed on theoverall object 170. The detection results can also be sent to anexternal device such as a personal computer or the like, for example.With the personal computer, it is possible to perform various processesbased on the detection results.

Above, the photoconductive antenna, the terahertz wave generatingdevice, the camera, the imaging device, and the measuring device of thepresent invention were described based on the embodiments in thedrawings, but the present invention is not limited to this, and theconstitution of each part can be replaced with an item of anyconstitution having the same functions. It is also possible to add anyother constituent materials to the present invention.

Also, with the present invention, it is also possible to combine theconstitutions (features) of any two or more of the embodiments notedabove.

Also, with the aforementioned embodiments, an n type semiconductor layerwas used as the first conductive region, and a p type semiconductorlayer was used as the second conductive region, but with the presentinvention, this is not restricted to these, and it is also possible touse a p type semiconductor layer for the first conductive region and ann type semiconductor layer for the second conductive region.

Also, with the present invention, for the light source device, the lightpulse generator can be a separate unit.

A photoconductive antenna according to the embodiment is adapted togenerate terahertz waves when irradiated by pulsed light. Thephotoconductive antenna includes a first conductive region, a secondconductive region, and a semiconductor region. The first conductiveregion is made of a semiconductor material containing a first conductivetype impurity. The second conductive region is made of a semiconductormaterial containing a second conductive type impurity different from thefirst conductive type impurity. The second conductive region is spacedapart from the first conductive region to form a gap therebetween in atop plan view of the photoconductive antenna. The semiconductor regionis positioned in the gap between the first conductive region and thesecond conductive region in the top plan view, and made of asemiconductor material having a carrier density that is lower than acarrier density of the semiconductor material of the first conductivelayer or a carrier density of the semiconductor material of the secondconductive layer. An interfacial surface of the semiconductor regionpositioned in the gap is flush with a first interfacial surface of thefirst conductive region and a first interfacial surface of the secondconductive region. A second interfacial surface of the first conductiveregion positioned on an opposite side from the first interfacial surfaceand a second interfacial surface of the second conductive regionpositioned on an opposite side from the first interfacial surface arepositioned on the same side with respect to the interfacial surface ofthe semiconductor region positioned in the gap.

With this configuration, it is possible to make the electric fielddirection constant, and thus, it is possible to suppress variation inthe terahertz wave emission direction, making it possible to generatehigh intensity terahertz waves.

With the photoconductive antenna according to the embodiment of thepresent invention, the gap between the first conductive region and thesecond conductive region is preferably filled by the semiconductorregion.

With this configuration, it is possible to generate higher intensityterahertz waves.

The photoconductive antenna according to the embodiment of the presentinvention preferably further includes a first electrode disposed on thefirst conductive region and electrically connected to the firstconductive region with the first electrode having the same shape as thefirst conductive region in the top plan view.

With this configuration, it is possible to lower the contact resistanceof the first conductive region and the first electrode, making itpossible to reduce the power consumption.

The photoconductive antenna according to the embodiment of the presentinvention preferably further includes a second electrode disposed on thesecond conductive region and electrically connected to the secondconductive region, the second electrode having the same shape as thesecond conductive region in the top plan view.

With this configuration, it is possible to lower the contact resistancebetween the second conductive region and the second electrode, making itpossible to reduce the power consumption.

The photoconductive antenna according to the embodiment of the presentinvention preferably further includes an insulation region disposed overat least a portion of the interfacial surface of the semiconductorregion positioned in the gap between the first conductive region and thesecond conductive region in the top plan view.

With this configuration, it is possible to more reliably prevent theoccurrence of leaked current at the gap between the first conductiveregion and the second conductive region.

With the photoconductive antenna according to the embodiment of thepresent invention, the semiconductor material of the semiconductorregion is preferably a III-V compound.

With this configuration, it is possible to generate higher intensityterahertz waves.

A terahertz wave generating device according to the embodiment of thepresent invention includes the photoconductive antenna according to theembodiment, and a light source configured and arranged to generate thepulsed light.

With this configuration, it is possible to provide a terahertz wavegenerating device having the effects of the present invention.

A camera according to the embodiment of the present invention includesthe photoconductive antenna according to the embodiment, a light sourceconfigured and arranged to generate the pulsed light, and a terahertzwave detecting unit configured and arranged to detect the terahertzwaves emitted from the photoconductive antenna and reflected by anobject.

With this configuration, it is possible to provide a camera having theeffects of the present invention.

An imaging device according to the embodiment of the present inventionincludes the photoconductive antenna according to the embodiment, alight source configured and arranged to generate the pulsed light, aterahertz wave detecting unit configured and arranged to detect theterahertz waves emitted from the photoconductive antenna and transmittedthrough an object or reflected by the object, and an image forming unitconfigured and arranged to generate an image of the object based ondetection results of the terahertz wave detecting unit.

With this configuration, it is possible to provide an imaging devicehaving the effects of the present invention.

A measuring device according to the embodiment of the present inventionincludes the photoconductive antenna according to the embodiment, alight source configured and arranged to generate the pulsed light, aterahertz wave detecting unit configured and arranged to detect theterahertz waves emitted from the photoconductive antenna and transmittedthrough an object or reflected by the object, and a measuring unitconfigured and arranged to measure the object based on detection resultsof the terahertz wave detecting unit.

With this configuration, it is possible to provide a measuring devicehaving the effects of the present invention.

GENERAL INTERPRETATION OF TERMS

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Finally, terms of degree such as“substantially”, “about” and “approximately” as used herein mean areasonable amount of deviation of the modified term such that the endresult is not significantly changed. For example, these terms can beconstrued as including a deviation of at least ±5% of the modified termif this deviation would not negate the meaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A photoconductive antenna adapted to generateterahertz waves when irradiated by pulsed light, the photoconductiveantenna comprising: a semiconductor layer; a first conductive layerdisposed on a first surface of the semiconductor layer; a secondconductive layer disposed on the first surface of the semiconductorlayer with a prescribed gap being formed between the first conductivelayer and the second conductive layer; a first electrode electricallyconnected to the first conductive layer; and a second electrodeelectrically connected to the second conductive layer, wherein the firstconductive layer contains a first conductive type impurity, the secondconductive layer contains a second conductive type impurity, and thesemiconductor layer has a carrier density lower than a carrier densityof the first conductive layer or a carrier density of the secondconductive layer.
 2. The photoconductive antenna according to claim 1,wherein the first electrode has the same shape as the first conductivelayer in a top plan view, and the second electrode has the same shape asthe second conductive region in the top plan view.
 3. A terahertz wavegenerating device comprising: the photoconductive antenna according toclaim 2; and a light source configured and arranged to generate thepulsed light.
 4. A camera comprising: the photoconductive antennaaccording to claim 2; a light source configured and arranged to generatethe pulsed light; and a terahertz wave detecting unit configured andarranged to detect terahertz waves emitted from the photoconductiveantenna and reflected by an object.
 5. The photoconductive antennaaccording to claim 1, further comprising an insulation layer disposed onthe semiconductor layer in at least a portion within the prescribed gapbetween the first conductive layer and the second conductive layer in atop plan view.
 6. A terahertz wave generating device comprising: thephotoconductive antenna according to claim 5; and a light sourceconfigured and arranged to generate the pulsed light.
 7. A cameracomprising: the photoconductive antenna according to claim 5; a lightsource configured and arranged to generate the pulsed light; and aterahertz wave detecting unit configured and arranged to detectterahertz waves emitted from the photoconductive antenna and reflectedby an object.
 8. An imaging device comprising: the photoconductiveantenna according to claim 5; a light source configured and arranged togenerate the pulsed light; a terahertz wave detecting unit configuredand arranged to detect terahertz waves emitted from the photoconductiveantenna and transmitted through an object or reflected by the object;and an image forming unit configured and arranged to generate an imageof the object based on detection results of the terahertz wave detectingunit.
 9. The imaging device according to claim 8, wherein the imageforming unit is configured and arranged to generate the image of theobject using intensity of the terahertz waves detected by the terahertzwave detecting unit.
 10. A measuring device comprising: thephotoconductive antenna according to claim 5; a light source configuredand arranged to generate the pulsed light; a terahertz wave detectingunit configured and arranged to detect terahertz waves emitted from thephotoconductive antenna and transmitted through an object or reflectedby the object; and a measuring unit configured and arranged to measurethe object based on detection results of the terahertz wave detectingunit.
 11. The measuring device according to claim 10, wherein themeasuring unit is configured and arranged to measure the object usingintensity of the terahertz waves detected by the terahertz wavedetecting unit.
 12. The photoconductive antenna according to claim 1,wherein the semiconductor material of the semiconductor layer is a III-Vcompound.
 13. A terahertz wave generating device comprising: thephotoconductive antenna according to claim 12; and a light sourceconfigured and arranged to generate the pulsed light.
 14. A cameracomprising: the photoconductive antenna according to claim 12; a lightsource configured and arranged to generate the pulsed light; and aterahertz wave detecting unit configured and arranged to detectterahertz waves emitted from the photoconductive antenna and reflectedby an object.
 15. A terahertz wave generating device comprising: thephotoconductive antenna according to claim 1; and a light sourceconfigured and arranged to generate the pulsed light.
 16. A cameracomprising: the photoconductive antenna according to claim 1; a lightsource configured and arranged to generate the pulsed light; and aterahertz wave detecting unit configured and arranged to detectterahertz waves emitted from the photoconductive antenna and reflectedby an object.
 17. An imaging device comprising: the photoconductiveantenna according to claim 1; a light source configured and arranged togenerate the pulsed light; a terahertz wave detecting unit configuredand arranged to detect terahertz waves emitted from the photoconductiveantenna and transmitted through an object or reflected by the object;and an image forming unit configured and arranged to generate an imageof the object based on detection results of the terahertz wave detectingunit.
 18. The imaging device according to claim 17, wherein the imageforming unit is configured and arranged to generate the image of theobject using intensity of the terahertz waves detected by the terahertzwave detecting unit.
 19. A measuring device comprising: thephotoconductive antenna according to claim 1; a light source configuredand arranged to generate the pulsed light; a terahertz wave detectingunit configured and arranged to detect terahertz waves emitted from thephotoconductive antenna and transmitted through an object or reflectedby the object; and a measuring unit configured and arranged to measurethe object based on detection results of the terahertz wave detectingunit.
 20. The measuring device according to claim 19, wherein themeasuring unit is configured and arranged to measure the object usingintensity of the terahertz waves detected by the terahertz wavedetecting unit.